Orthogonal mode transducer



Oct. 10, 1961 Filed July 1, 1958 R. L. FOGEL ORTHOGONAL MODE TRANSDUCER 3 Sheets-Sheet 1 W/a/zaz 1655474. Fay 1:2,

Oct. 10, 1961 R. L. FOGEL 3,004,228

ORTHOGONAL MODE TRANSDUCER Filed July 1, 1958 s Sheets-Sheet 2 i w flneW/ai fa s/e71. Feasz Oct. 10, 1961 R. FOGEL 3,004,228

ORTHOGONAL MODE TRANSDUCER Filed July 1, 1958 5 Sheets-Sheet 3 United States Patent 9 3,004,228 ORTHOGONAL MODE TRANSDUCER Robert L. Fogel, Torrance, Calif assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed July 1, 1958, Ser. No. 745,933 3 Claims. (Cl. 33321) This invention relates to microwave energy coupling devices, and particularly to devices for coupling modes of energy which are orthogonal with respect to each other between indiw'dual energy transmission lines and a common transmission line.

In microwave systems it is often desirable to have an electromagnetic wave energy transmission line, such as a waveguide, which will support two energy modes which are orthogonal with respect to each other. Square waveguides, for example, may be used to conduct energy in either of two modes whose electric vectors are normal to each other. The electric vectors may be, but need not be, normal to the waveguide walls. When such orthogonal mode transmission lines are employed, it is necessary to have some means of transferring energy into and out of the common transmission line in the individual modes or in both modes simultaneously. Devices for this purpose are usually termed orthogonal mode transducers. The manner in which these devices operate is to transfer energy in a first mode between one individual arm and the common arm, and to transfer energy in a Second mode, orthogonal to'the first, between a second arm and the common arm. The transfer is effected in each case in both directions of propagation.

A number of devices for fulfilling this function are known and in use. One of the most eiiective of such devices is an orthogonal mode transducer which employs a square waveguide body for .the common arm and which has a first rectangular waveguide colinear therewith as one individual arm and a. second rectangular waveguide normal thereto as the other individual arm. This arrangement provides the desired transfer of energy between the arms. The devices of this configuration heretofore constructed, however, have been subject to a number of operating difiiculties which in some instances are incompatible with systems applications. For one thing, reflectioneifects have often increased the voltage standing wave ratio (VSWR) to an excessive level. Further, there has not been pure energy coupling of each of the modes, some of the energy instead being transferred out the wrong arm. A number of transducers of this type, particularly those which employ probes for coupling energy, are frequency sensitive and accordingly suifer from high VSWR at other than a central frequency. Other such devices are known, but these principally have a circular waveguide for the common transmission line, and accordingly are not applicable in the many situations in which it is desired to employ asquare waveguide for the common waveguide. The 'broadestapplication for Orthogonal mode transducers involves the transmission of dominant TE modes in a square waveguide in which electric vectors are nor- 'mal to the waveguide walls. Other dominant modes may,

however, be transmitted along a square waveguide. The same requirements may exist for coupling energy in such modes into and out of separate arms extending from the common square waveguide.

proved microwave device for transferringenergy between a common transmission line and one of two individual arms, dependent uponthe mode of the energy provided.

A further object of this invention is to provide an improved orthogonal modetransducer for coupling energy to and from a square waveguide, which device has higher efficiency, greater broad bandedness and lower VSWR than the devices of the prior art.

A further object of this invention is to provide an improved orthogonal mode transducer for coupling energy between one square and two rectangular waveguides, which device operates with high efiiciency and at the same time is simple to fabricate.

A further object of this invention is to provide an improved orthogonal mode transducer for operating at high powers and with more complete separation of the modes than has heretofore been possible. q

These and other objects of this invention are achieved by an arrangement illustrative of the invention for coupling energy between a square waveguide and one rectangular arm colinear therewith or a side rectangular arm normal thereto. Energy in one dominant mode is transferred substantially without reflection or losses between the square waveguide and the colinear arm. Energy in the other dominant mode is transferred with like efficiency between the side arm and the square waveguide through a coupling aperture in a side wall of the square waveguide. Desirable operative characteristics are achieved through the combined use of a number of features. A transition section may be used between the square waveguide and the colinear arm, and a metal septum may be used within the transition section. Energy may be coupled into the side arm through a coupling aperture, and the side arm may also contain metallic irises at spaced points. By observing particular relationships between the position and configuration of the aperture, irises, septum and transition sections, the energy coupled in the various modes and directions through the transducer is maintained substantially at full strength and free from reflections, and is not directed into the wrong arm. The arrangement may be employed with orthogonal modes which are normal to the square waveguide or diagonally disposed with respect to the square waveguide.

The novel features of this invention, as well as the invention itself, both as to its organization and method of operation, may best be understood when considered in the light of the following description, when taken in connection with the accompanying drawings, in which like reference numerals refer to like parts, and in which:

FIG. 1 is a perspective view, partly broken away, of an orthogonal mode transducer for transferring the dominant TE modes in accordance with this invention;

FIG. 2 is a plan view, partly broken away, of the arrangement of FIG. 1;

FIG. 3 'is a side elevation View of the arrangement of FIG. 1;

FIG. 4 is an and elevation view of the square waveguide end of the arrangement shown;

FIG. 5 is a perspective view, partly broken away, of an alternative transducer forv operation, with orthogonal modes in which the electric vectors lie along the diagonals of a square waveguide, and

FIG. 6 is an end view of the arrangement of FIG. 5.

An orthogonal mode transducer in accordance .with the invention, referring now to FIGS. 1 through 4, utilizes a main waveguide body 10 having a square Waveguide section 20 at oneend and a first rectangular waveguide section 30 at the other end with a transition section40 intermediate the square waveguide section 20 and the first rectangular waveguide 30. The first rectangular waveguide 20 may also. be called the colinear arm,3 0. For purposes of convenience herein, the square waveguide 20 will be said to have opposite first and third walls 21 and 23 respectively. The first and third walls, 21 and 23 respectively, are the side walls of the square waveguide section 20, with the position shown in the figures being used --todefine the frame of reference. It will of course be understood 'that snob -designations: are used only to simplify the descriptio'nmime-arrangement and that the body-'10 may be used in any relativeposition. The square waveguide section 20-theref0re also includes a second wall 22 and a fourth-wa-ll 24,- which;are opposite to each other and are the top andbottonrwalls respectively of the square -waveguide section-20z As thusviewed, the first WaIl' ZIWcontains'a rectangular coupling aperture or slot 26 centrally disposed-therein and having its direction of elongation parallelto the longitudinal of the square waveguide section 20.

A- 'useful'feature of'this arrangement is that the top and bottomwalls 22,' 24-ofthe square-waveguide section may each be coplanar and integral with-the corresponding wall of the transition :section -40and the first rectangular waveguide section or colinear arm 30. In the arrangementthus enstructed,'the narrow walls 31, 32

of the colinear arm 30 are coplanar with the top and bottom walls 22, 24 ot the square waveguide section 20. The broad wal'ls'33, 34-of the colinear arm 30 lie in planes parallel to the planes of the sidewalls 21, 23 of the square waveguide 20;- The walls 33, 34 are, however, coupled through successively stepped down edges 41, 42 in the transition section 40, to the more widely spaced sidewalls 21, 23, of the. square waveguide 20. The step down edges 41,242" in the transition section 40 form a successive pair ofquarter Wave transformers between the square waveguidesection 20' and the colinear arm 34 It maybe seen, therefore, that the square waveguide section. 20, the first rectangular waveguide section 30 and the intermediate transition section 40 lie along the same axis and that they may be formed as an integral body having planar topand bottom walls. The structure may also include terminal flanges coupled individually to the free end portions of each of the waveguide sections. Thus the square wavegui e ction. may inclu a quare Waveguide flange 28 and the COIinear .arm 30 may includel n associated colineararm flange 38.

Positionedjwithin the. transition section 40 ,is a con ductive metal septum 44- or plate..bisecting the transition section 40 along a planeparallel to ,theplanes of the broad .walls .33, 34 of the col-,inear arm 40. The metal septum .44. extends. between thetopandbottom Walls of the transition Section40 and :along the axis of the square waveguidelfl. and the-colinear; arm 30.

In axial length, the metal septum 44 mayextend approximately coextensively with thelength of. the transition section 40. The edge of. the septum 44 which is closest to the square waveguide 2ll5lies approximately alongtheplane defined by the interiorsurfacesof thefirststep down edges-41. The septum 44 may be afi'xed entirely Withinthe body section or may fit through a slot in the body'10 walls and be attached thereto by solder.

A second rectangular, waveguide section or side arm 50 is coupled to the. first side. Wall 211 of the square waveguide. section and. encompasses the. coupling aperture 26.. Thenarrow wallsSl, 52- o-fthe side arm 50 are substantially normal to the. axis of the square waveguide 20, and the broad walls 53, 54 aresubstantially parallel to the.- axis of the. main body section 10 and to the narrow walls,.31, 32 .of .the colinear arm 30. Thustheside arm 50 is..nor mal to the square waveguide 20 and has its heightdimension in a plane normal to the height dimensionof the colinear. arm 30. Thesecond rectangular waveguide 50rmayinc1ude. aside arm flange 58 at the uncoupled end thereof for attachment .to external devices (not shown).

A' pair of elongated met llic irisesfifl, .61 are aflixed within the side arm 'at the side arm flange, 58; Each f he me allic ris 6 6 i adjacent a differ nt n rrow Wall 51', 52' of the side arm 50, and each of the irises 4 60, 61 has itsdirection of elongation substantially parallel to the adjacent narrow wall 51 or 52. Together the irises 60, 61 form an inductive reactive element in the path of energy transmitted along the side arm 50. As may be best seen in FIG. 1,-the inductive irises 60, 61 may be set intorecessed portions in the associated walls of the side arm 50,. so as to be flush withthe surface of the side arm flange 58. The arrangementshown is merely one useful configuration. If the side arm 50 were of greater length, the irises 60, 61 could be afiixed in it through slots (not shown) in each of the narrow walls 51, 52.

The arrangementofFIGS. 1 through .4 isintended to operate with the dominant TE modes'of microwaveenorgy in a square Waveguides A first of these dominant modes will, for purposes of reference, be-taken-tobe that in which the -electric vectorris. vertical, as. viewed in the figures. Such energy therefore-is to be transferred in either direction, dependingupon the-source, between the side arm 50 and the square'waveguide 20.v The second dominant mode; therefore,; is thatin which the electric vector is horizontal, as viewed in the figures,- and which is therefore'transferred ineither direction between the square-waveguide 20 and the colinear arm 30'.- In each of the rectangular'waveguid'es 30, 50 the dominant mode is also the TE mode.

As above described, electromagnetic wave'energy inputs maybe provided to the square waveguide 20 in either or both modes, or individually, in the particular mode supported, to'the side arm 50 or-the colineararm 39. Assuming, for purposes of description, that the square waveguide 20 isto be used as-the input, outputs from the device will therefore beprovided from the side arm 59 or the co linear arm-30. These outputs are desirably at full amplitude in the correct arm, with substantially no energy being coupled out the other-arm. It may be seen that the electric vector of energy'in the first dominant mode is normalto the broad walls '53, 54 of the sidearm 50. Thus such energy should be supported by the side arm 56, but not the perpendicularly disposed colinear arm30. Conversely, energy in the second dominant mode should be supported as the TE mode in the colinear arm 30 but not in the side arm 50. It will also be appreciated by those skilled in the art, however, that the abrupt discontinuities involved, effectively prevent proper coupling of, energy between the. various armsand that, without more, power loss, reflections and unwanted energy propagation would occur.

The manner in which this arrangement operates to sub stantially minimize VSWR and to increase coupling efliciencies over a broad frequency band will now be de scribed. The presence of the .metal septum 44 in the transition section 40 .providesa conductive member which acts as a short circuit for the first dominant mode but which is substantially electromagnetically transparent to the second dominant mode. The leading edge of the metal septum 44 presented to energy transmitted along the square waveguide 20 toward the colinear arm 30, however, should be placed carefully with respect to. the first step down edge-4 1 of the transition section 40 and with respect to the coupling aperture 26 and the metallic irises 60, 61. It has been found that best results are achieved in this arrangement when the leading edge of the conductive septum 44 lies approximately in the plane of the interior surfaces of the first step down edges 41 of the transition section 40.: When the metal septum 44 is thus placed the short circuit presented to energy in the first dominant mode provides maximum coupling into the side arm 50. Further, when the septum 44 is so placed a compensating inductive reactance may be introduced in the .side arm 50.-by the metallic irises 60, 61 in the path of the electromagnetic wave energy in the. first dominant mode. Energy iscoupled intothe. side 50 because currents in the .firstwall 21 of the square waveguide 20 are interrupted by the coupling aperture 26,

which is thereby excited. Note, however, that the coupling aperture 26 has dimensions which are less than the transverse dimensions of the side arm 50. As a consequence, the coupling aperture 26 may be considered to present both capacitive and inductive reactance to the energy coupled into the side arm 50. The reactive components thus introduced may be chosen with respect to the other elements so that substantially complete elimination of reflections is obtained. It will be understood, therefore, that the selective use of the inductive irises 60, 61 spaced apart from the reduced coupling aperture 26, together with the metal septum 44 provides substantially complete coupling, without reflections, of energy in the first dominant mode between the square waveguide 20 and the side arm 50.

Energy in the second dominant mode, whose electric vector is normal to the metal septum 44 and normal to the plane of the coupling aperture 26, is transmitted directly through the main waveguide body 'to the colinear arm 30 without being coupled out the side arm. 50. Currents in the first wall 21 of the square waveguide section 20 are along the length of the coupling aperture 26. The coupling aperture 26, however, is relatively narrow in the direction transverse to the longitudinal axis of the square waveguide 20 and is centered about that longitudinal axis. Accordingly, energy in the second dominant mode does not excite the coupling aperture 26 and accordingly does not couple through the coupling aperture 26 into the side arm 50. The presence of the metal septum 44 in the transition section 40 does not affect the second dominant mode except to provide a small ,capacitive susceptance to this mode. In this connection, the transition section serves, in conjunction with the coupling aperture 26, and the metal septum 44 to maintain at a minimum the reflections in the second dominant mode due to the transistion between the square Waveguide section 20 and the colinear arm 30.

Energy provided from the side arm or the colinear arm 30 as input is similarly coupled through the square waveguide 20 without substantially any coupling of energy into the opposite rectangular arm 30 or 50. V The design of an orthogonal mode transducer in this fashion makes possible the achievement of VSWRs of less than 1.10 over a 15% bandwidth.

It should also be noted that the structure thus provided is extremely simple to construct and of a rugged nature. The main waveguide body 10 may be 'constructed'as an integral piece, for example, and may thus be formed simply, without further need for precise adjustments. To this structure may be added a side arm 50 of standard characteristics. The metallic irises 60, 61 and the metal septum 44 are extremely simple to construct and to place in the desired configuration.

Another and different arrangement in accordance with the invention is shown in FIGS. 5 and 6. In some applications a square waveguide may be used to transmit energy in modes in which the electric vectors lie along the diagonals of the square waveguide. Such modes may be induced, for example, by application of a 45 rotation to energy maintained in the TB modes. Such diagonally supported modes are independent and orthogonal with respect to each other. They may be considered to be another form of dominant mode, or at least quasidominant. It is often desired to couple energy from such modes into perpendicularly related rectangular waveguides, and such purposes are fulfilled by the arrangement shown in FIGS. 5 and '6, to which reference is now made. It should be noted that the arrangement of FIGS. 5 and 6 is depicted for greatest clarity, and is not drawn to scale.

In this arrangement, a metal septum 44' is placed within a square waveguide 20' along one of the diagonals thereof. The square waveguide 20' includes a coupling aperture 26' along one of its edges other than the edges contacted by the metal septum 44', the coupling aperture 26' having its direction of elongation along the longitudinal axis of the square waveguide 20'. A side arm 50', having'its axis normal to that of the square waveguide 20', and to the plane of the septum 44' is coupled to the square waveguide 20 about the coupling aperture 26 therein. In this instance, the coupling aperture 26' may have the same width, or narrow dimension as the asso ciated side arm 50'. The length of the coupling aperture 26', however, may be less than the broad wall dimension of the side arm 50' so that inductive irises are thus definedat the aperture 26'. The septum 44 may have its leading edge (as to energy transmitted from the free end. of the square waveguide 20') positioned in a plane passing adjacent the trailing edge of the coupling aperture 26'. vThe broad walls of the side arm 50' are parallel to the longitudinal axis of the square waveguide 20.

Spaced apart'from the coupling aperture or slot 26' the narrow walls of the side arm 50' each include a side slot in which is positioned a conductive metallic iris 60 or 61'. These irises 60', 61 provide inductive reactances to energy in the side arm 50'.

A transition section 40' is defined by successive stepped sections46, 47, 48 coupling from the square waveguide ,20 to a colinear arm 30' which is diagonal with respect thereto. The colinear arm 30' therefore has its broad walls parallel to the plane of the metal septum 44'.

In accordance with the considerations provided with respect to. FIG. 1, the relationship of the irises 60', 61', the transition section 40', the coupling slot 26 and the septum. 447 may be selected with relation to each other for best energy coupling and least energy reflection.

Inpoperation, energy in afirst orthogonal mode diagonally supported within the square waveguide 20 will be taken, for purposes of description, to be parallel to the metal septum 44. Energy in the second of these orthogonalmodes will be taken to be normal to the metal septum 44'. As previously described, the energy in the first diagonally supported mode in the square waveguide 20' sees the metal septum 44 as a short circuit. Such energy also excites the coupling slot 26, so that energy is coupled into the side arm 50', with the inductive elements at the coupling slot 26', and the inductive irises 60', 61 positioned within the side arm 50 minimizing the reflected energy to maintain an extremely low VSWR.

As a consequence, in the first diagonally supported mode no energy is transmitted out the colinear arm 30, and substantially full energy is transmitted out the side arm 50.

Energy in the. second diagonally polarized mode coupled through the square waveguide 20' does not excite the coupling slot 26' and is substantially unaffected by the metal septum 44, so that such energy is transmitted through the transition section 40" to the colinear waveguide arm 30'. Again, the metal septum 44' provides only a small capacitive susceptance, and the transition section 40' provides transfer of energy into the colinear arm 30 without appreciable reflection efiects. Like considerations prevail, and like efliciency is again obtained, for couplings of energy in the directions from the side arm 50' or the colinear arm 30' to the square waveguide 20.

An example of the orthogonal mode transducer of FIGS. 1 through 4 may employ the following dimensions:

Square waveguide 0.800" x 0.800" (cross section). Side arm 0.400" x 0.900" (cross section).

Colinear arm 0.450" x 0.800" (cross section). Coupling aperture 0.155" x 0.765".

Metal septum 0.600" long x 0.032" thick.

Irises 0.013" (transverse to waveguide).

Transition section 0.700 (transverse dimension). Transition section 0.575" (between successive steps).

Thus there has been described an improved orthogonal mode transducer for microwave applications. The device is simply constructed, but provides substantially complete transfer of energy between a square waveguide andindividual ones of two perpendicularly related rectangular waveguides, without the transfer of undesired energy to the other of the. rectangular waveguides; The reflections in this device are kept to a minimum-and the characte'ristics thus achieved are maintained over a broad frequency band.

I claim:

1. An orthogonal mode transducer comprising a square waveguide capable of supporting first and second modes of energy wherein the electric fields thereof. are orthogonally. disposed with respect to eachother, a first rectangular waveguide disposed in substantial axial alignment with said square waveguide, a second rectangular waveguidecoupled to said square. waveguide substantially normally to the axis thereof by means of a rectangular aperture openinginto said square waveguide", said aperture having the longest dimension thereof parallel to theaxis of said square waveguide whereby only energy in the first of said modes willbe coupled into said secondrectangular waveguide, the broad walls and the narrow walls of said second rectangularwaveguide being disposed substantially normal to the broad walls and .the narrow walls" of said first rectangular waveguide, respectively, a transition section disposed between said first rectangular waveguide and said square waveguide for .couplinglsaid square waveguide to said first rectangular waveguide, 'said transition section includingsuccessively stepped portions eiiective to vary one of the transversedimensions of said section between those ofsaid'square waveguide and of said first rectangular waveguide whereby energy in the second of said modes will be coupled between said square waveguide and said first rectangular waveguide, means disposed within said transition section to prevent energy in said first mode from enteringsaid first waveguide.

2. An. orthogonal mode transducer-comprising. a square waveguide capable of 'supportingpfirst and second modes of energy wherein the electric fields thereof are orthogonally disposed with respect to each other, a first'rectangular waveguide disposed in substantial. axial alignment with said square waveguide section, said rectangular waveguide havinga pair of narrow-walls disposed substantially coplanar with a firstpair of side walls of said square waveguide, said rectangular waveguide having broad walls disposed substantially parallel to the other pair of sidewalls of said rectangular waveguide, a transition section coupling said square waveguide to said rectangular waveguide, said transition section including successively stepped portions coupling the broad walls'of said first rectangular waveguideto saidv other pair of side walls of said square waveguide whereby energyin the first of. said" modes willbe coupled between said squarewa'veguide and said first rectangular waveguide, a septum disposed'within saidftransition'sectionto prevent energy, in the 'second'of sai'd'ino'des from: entering said first rectangularjwaveguide, a second rectangular waveguide coupled tc'said square "waveguide substantially normally to the axis 'thereof by means of a rectangular: aperture in one ofsaid second pair of said'side walls, said aperture having the narrow "dimension thereof transverse of said sidewall and "the longidin'i'ensionthereof parallel'to the axis of said square waveguide. whereby only energy in said secondrnode' wili'be coupled into said second rectangular waveguide, the broad walls and the narrow walls of'said second rectangular waveguide being disposed substantially normal to the broad walls and the narrow walls of said "first rectangular waveguide; respectively.

3. An orthogonal mode transducer'comprising a square waveguideicapable of'supporting first and second" modes of energy 'wherein'theelectric' fields thereof are orthogonally disposed with respect toeach'other, a first rectangular waveguide disposed in substantial axial alignment with said square waveguide, said rectangular waveguide having a pair of narrow walls and a pair'of broad walls that are; disposed substantially parallel'to the diagonals of said square waveguide section; a transition section couplingsaidsquarejwaveguide' to said rectangular waveguide whereby energy in the first of said modes will be propagated in said first rectangular waveguide, said transition section -comprising a number of successively stepped portions-positioned along the longitudinal axis of said square waveguide so as to progressively change a transverse dirne'nsion between'that of a diagonal and that of said narrow walls, a septum disposed in said transition section normal to said last mentioned diagonal forreflect- References Cited in the-file of this patent UNITEDSTATES PATENTS 2,682,610." King June 29, 1954 2,764,740 Pratt". Sept. 25, 1956 2,840,787" Adcock: June 24, 1958 2,853,683 Murphy Sept. 23, 1958 2',-908;872 Garofin. Oct. 13, 1959 

